That seems a bit strange, given that the release is after the Plextor Premium (52/32/52). Plextor Europe recently released an external USB 2.0 version of the Premium (called Premium-U) well after their release of the Plextor Premium ATAPI drive. The Premium-U has yet to be released here in the U.S. and it may be a while before the Plextor 52/24/52A shows up here in the U.S. Also, Plextor Europe released an external USB 2.0/Firewire (both interfaces) version of their PX-504 DVD burner called the PX-504UF.

Ian wrote:I think the 52/24/52A is marketed more at general consumers where the Premium is more for the "professional".

That was pretty much how I understand it too--I presumed that Plextor released the 52/24/52A as a lower cost alternative to the Premium. Also, the 52/24/52A appears to be the replacement for the 48/24/48A. So the 52/24/52A would be targeted at general consumers, or consumers who didn't want to spend the extra money for the Premium.
Just a quick note: the Plextor Premium (ATAPI version) has already started being sold at Best Buy retail stores here in the U.S.